(1) Field of the invention
The present invention generally relates to a cordless phone and a cordless phone system using such cordless phone, and more particularly to a cordless phone and a cordless phone system in which an extension communication between cordless phones and control of domestic electric equipments can be performed.
(2) Description of related art
Recently, demand for cordless phones has been rapidly grown because of the convenience thereof. There is a case where many cordless phones are used in a large office. In addition, a cordless phone system has been also proposed in which a plurality of cordless phones are connected to a PBX so that an extension communication between the cordless phones, general calling to the cordless phones, a paging operation, calls to other stations via an outside line, data transmission and so on can be performed. There is a desire for simple and high performance cordless phone systems to be used in small offices and homes.
FIG. 1 shows a conventional cordless phone. Referring to FIG. 1, a cordless phone is constituted of a base station 1 and a personal station 16. The base station 1 has a local line interface 2, a personal station interface 8, a channel switch 6, a tone signal source 7 generating tone signals such as a ringing tone signal (RT), and controller 15. The channel switch 6 selectively makes a channel between the local line interface 2 and the personal station interface 8 and a channel between the tone signal source 7 and the personal station interface 8. The local line interface 2 is connected to a local line and has a hook circuit 3 (F) performing an open/close control of a loop, a call detecting circuit 4 for detecting a calling signal and a sender 5 sending dialing signals (push-button signals). The personal station interface 8 has a voice-band processing circuit 9, a mixer 10, a radio unit 11 including a control channel and a voice channel, an MSK modem 12 and a data transmitter-receiver 13 connected to an antenna 14. The MSK modem 12 converts 1/0 digital signals respectively into 1200/1800 Hz analog signals and vice versa. The controller 15 controls the local interface 2, the channel switch 6 and the personal station interface 8.
When a calling signal transmitted via the local line is received by the base station 1, a detecting signal C output from the call detecting circuit 4 is supplied to the controller 15. The controller 15 supplies the lamp signal L and a switching signal S respectively to the personal station interface 8 and the channel switch 6. Due to the switching signal S, the channel switch 6 makes a channel connecting the tone signal source 7 to the personal station interface 8 so that the tone ringer signal (TR) is supplied to the personal station interface 8. The lamp signal L is converted into an analog signal by the MSK modem 12 and supplied to the radio unit 11 via the mixer 10. Then the lamp signal L is transmitted from the control channel of the radio unit 11 to the personal station 16. As a result, a calling lamp of the personal station 16 is turned on. A frequency band of the tone ringer signal (TR) is limited to a predetermined band by the voice-band processing circuit 9, and mixed with an MKS signal by the mixer 10. A signal corresponding to the tone ringer signal (TR) is supplied from the mixer 10 to the radio unit 11, and transmitted via the voice channel of the radio unit 11 to the personal station 16. As a result, a tone ringer is made to ring in the personal station 16. At this time, when an off-hook operation of the personal station 16 occurs, an off-hook signal F is supplied to the controller 15 via the data transmitter/receiver 13. The controller 15 causes the hook circuit 3 to be in an off-hook state and supplies a switching signal to the channel switch 6. The channel switch 6 makes a channel between the local line interface 2 and the personal station interface 8, so that communication between the personal station 16 and calling station can be performed via the base station 1.
In a case where the personal station 16 calls another station, first, an off-hook operation of the personal station is carried out. The off-hook signal depending on the off-hook operation F is transmitted from the personal station 16 to the base station 1 by radio and supplied to the controller 15 via the data transmitter/receiver 13. The controller 15 causes the hook circuit 3 to be in the off-hook state and supplies a switching signal S to the channel switch so that the channel between the local line interface 2 and the personal station interface 8 is formed. Under this condition, an operator of the personal station 16 recognizes a dial tone and carries out a dialling operation. Dial data D depending on the dialling operation in the personal station 16 is supplied to the controller 15 via the data transmitter/receiver 13. The controller 15 supplies the dial data D to the sender 5 and the sender 5 supplies a dialling signal corresponding to the dial data D to the local line.
The above conventional cordless phone can carry out communication with an external station via an outside line (the local line). However, in a system having a plurality of the above conventional cordless telephones, extension communication between the cordless telephones cannot be performed. If the base station 1 is constituted so that a plurality of personal stations 16 are coupled thereto, extension communication between personal stations 16 can be performed via the base station 1. However, in this case, the number of channels which can be provided in the base station 1 and an area where radio communication between personal stations and the base station 1 can be performed are limited, and the cost thereof increases.
FIG. 2 shows a conventional telephone exchange system using a PBX. Referring to FIG. 2, two cordless phones are connected to a PBX 21. The cordless phones are constituted of base stations 1 and 1' and personal stations 16 and 16'. The PBX 21 has line circuits 22 connected to the base stations 1 and 1' of the cordless phones, a digital exchange network 29, a trunk circuit 30 and a controller 33. Each of the line circuits 22 accommodates a 2W subscriber line connected to the base station 1 (1') of a corresponding cordless phone. Each of the line circuits 22 has a loop detecting circuit 23, a battery feed and ringing circuit 24, a terminating circuit 25 of the subscriber line, a 2-to-4 wire converter 26, a coder 27 and a decoder 28. The trunk circuit 30 has a DC detecting circuit 31 and a loop open/close circuit 32. The trunk circuit 30 has also the terminating circuit 25 of a local line, the 2-to-4 wire converter 26, the coder 27 and the decoder 28 in the same manner as each of the line circuits 22. The PBX 21 can be connected with analog telephones, digital telephones and domestic electric equipments controlled by the digital telephone. The controller 33 controls the line circuits 22, the exchange network 29 and the trunk circuit 30.
In the conventional telephone exchanging system shown in FIG. 2, when a first cordless phone calls a second cordless phone, the PBX 21 forms a channel between the base station 1 of the first cordless phone and the base station 1' of the second cordless phone. As a result, an extension communication between the first and second cordless phones can be carried out via the PBX 21.
In the PBX 21, the battery feed and ringing circuit 24 must supply a voltage of 48v to the 2W-subscriber line so that a loop current in a rage of 10-30 mA is supplied to the 2-W subscriber line. Under this condition of the PBX 21, each of the cordless phones can be normally operated. This condition is the same as that to be satisfied in an exchange provided in a public communication network. The PBX satisfying the above condition is expensive, so that it is difficult to introduce the PBX to a system used for small offices and homes.
Due to decreasing the voltage supplied to the 2W-subscriber line and to limitation of the current supplied to the 2W-subscriber line, the cost of the PBX can decrease. Such PBX is often referred to as a simplified switching unit. However, in the system provided with the simplified switching unit, electrical characteristics thereof are sacrificed for the cost. In addition, a degree of decreasing of the cost is small.